Obviously, 225 days is nothing like 9 months. Your wording is unclear, but making just Plain crisps for 225 days will use 225 × 0.82 potatoes = 184.5 potatoes. Hence you need to ensure that any use of the other 1274.5 potatoes doesn't consume more than that. For example, you could make just Ridged crisps for up to 1274.5/3.2 days = 398.28125 days.

This has nothing to do with trigonometry. It seems to be just basic arithmetic.